The present invention relates generally to printing, and more particularly to ink jet printing, wherein images are formed on a print medium by propelling droplets of ink toward the medium in a controlled fashion. Still more particularly, the invention pertains to an improved ink jet printing cartridge for use in an ink jet printing device.
Ink jet printers has proven useful for reducing computer generated text and graphics images to printed form. They produce images having higher quality than dot matrix printers and are generally faster. At the heart of the ink jet printer is a cartridge, known in the art as an "ink jet cartridge", that contains a reservoir of ink and an electro-mechanical system for propelling the ink toward a print medium in a controlled fashion. The electro-mechanical system typically includes a discharge plate located at one end of the ink reservoir having one or more vertical rows of very small ink discharge ports therein in fluid communication with the ink reservoir. At each discharge port there is placed an ink propulsion element such as a piezoelectric pump or a conductive heating element. Each propulsion element is connected to a conductive path element formed on a carrier strip that is mounted on an outside surface of the ink reservoir. The carrier strip has a plurality of conductive circuit paths formed thereon, much like a printed circuit board except that the carrier strip may be flexible. Each circuit path extends from a single ink propulsion element of the discharge plate to an electrical contact.
When the ink jet cartridge is properly positioned in the printer, the electrical contacts engage corresponding output pins in the printer. Images are formed by providing electrical signals to selected combinations of the output pins of the printer. These signals are in turned carried to the associated ink propulsion elements at the ink discharge ports. The activated ink propulsion elements exert or generate a force, e.g. by heating, that causes the ink drops to spray toward the medium in a predetermined pattern. By selective activation of the printer output pins, numerous ink patterns can be formed on the medium.
As ink jet cartridges age, the quality of the images they produce can deteriorate. After prolonged use, one or more conductive elements may cease functioning, such that no ink is expelled from the corresponding ink discharge ports. When this condition occurs, gaps appear in the generated image. This problem has been aggravated in recent years as a result of recycling efforts wherein spent ink cartridges are refilled with ink for continued use, thus extending the active life of the cartridge.
It would be desirable, therefore, to provide an improved ink jet cartridge whose image producing capacity does not deteriorate over time or which deteriorates at a slower rate. In that way, the useful life of the cartridge could be extended to provide more service to the user and thus more of an incentive to recycle.